1. Field of the Invention
The present invention relates to a highly water resistant composition that comprises a specific modified polyvinyl alcohol and an organotitanium compound having a chelating ligand, and to a coating agent and a recording material such as a thermal recording material, an ink-jet recording material, etc.
2. Description of the Related Art
Heretofore, a polyvinyl alcohol (hereinafter referred to as PVA) is widely used for various binders, adhesives and surface-treating agents. It is known that PVA has excellent properties of film formability and mechanical strength and is far better than any other water-soluble resins. However, as being soluble in water, PVA is problematic in that its water resistance, especially when dried at low temperatures is poor. To solve the problem, various methods have heretofore been investigated. For example, one method known in the art comprises crosslinking PVA with any of glyoxal, glutaraldehyde, dialdehyde starch, water-soluble epoxy compounds, methylol compounds, etc. However, the method requires high-temperature long-time heat treatment at 100xc2x0 C. or higher, often at 120xc2x0 C. or higher, to ensure PVA of satisfactory water resistance. For obtaining PVA which could be still water resistant even when dried at low temperatures, known is a method of processing PVA under a strong acidic condition, for example, at pH of not higher than 2. However, PVA obtained in the method is problematic in that the viscosity of its aqueous solution is unstable and the solution often gels while handled, and that its water resistance is unsatisfactory. Another problem with the method is that PVA processed under such a severe condition is discolored and the appearance of its film is poor. Further known are a method of crosslinking a carboxyl group-having PVA with a polyamidoepichlorohydrin resin; and a method of crosslinking an acetoacetyl group-having PVA with a polyaldehyde compound such as glyoxal or the like. However, these still have some problems. The former requires a large amount of a polyamidoepichlorohydrin resin for ensuring PVA of satisfactory water resistance. In the latter, PVA produced could have good water resistance, but the viscosity of its aqueous solution is extremely unstable. In addition, using such a polyamidoepichlorohydrin resin and a polyaldehyde is unfavorable for safety.
Still another method is known for obtaining water resistant PVA, which comprises adding a titanium lactate to an aqueous composition containing PVA (see Japanese Patent Laid-Open No. 94768/1974). However, this also has some problems. Concretely, when the PVA composition is shaped into sheets, or is applied onto substrates to form PVA-coated sheets, and when the sheets are processed at relatively low temperatures around room temperature, the thus-processed sheets are degraded in boiling water, as so demonstrated in Comparative Example 1 given hereinunder. This means that the water resistance of PVA processed according to the method is not satisfactory. In addition, the viscosity of an aqueous solution of the titanium lactate-containing PVA is unstable at low temperatures.
Also known is adding a filler such as titanium oxide or the like to a thermal recording material that comprises a modified PVA having an ethylene unit content of from 3 to 15 mol % with alkali metal ions being added thereto (see Japanese Patent Laid-Open No. 24016/1997). However, even though containing titanium oxide added thereto, the water resistance of the PVA film is still extremely poor, as so demonstrated in Comparative Example 4 given hereinunder.
Also known is an adhesive that comprises a modified PVA having an ethylene unit content of from 1 to 24 mol % with an inorganic filler such as titanium sulfate or the like being added thereto (see Japanese Patent Laid-Open No. 283682/1996). However, even though containing titanium sulfate added thereto, the water resistance of the PVA adhesive is still extremely poor, as so demonstrated in Comparative Example 5 given hereinunder.
One object of the present invention is to provide a water resistant composition, of which the film formed by itself or the coat layer formed on a substrate is highly resistant not only to cold water but also to warm water and hot water, even after dried or heat-treated at relatively low temperatures not higher than 70xc2x0 C., especially falling between room temperature and 50xc2x0 C., or even at around room temperature, and which is free from problems of viscosity stability and safety.
Another object of the invention is to provide a coating agent that comprises the composition.
Still another object is to provide a thermal recording material having a coat layer of the composition.
Still another object is to provide a recording material having an ink-absorbing layer of the composition, especially an ink-jet recording material having it, and also to provide such a recording material especially an ink-jet recording material in which the absorbent layer is a coat layer of the composition.
The objects of the invention are attained by providing a water resistant composition comprising (A) at least one selected from modified PVA containing from 1 to 20 mol % of xcex1-olefin units with not more than 4 carbon atoms, modified PVA containing from 0.01 to 1 mol % of silyl groups, and modified PVA containing from 1 to 20 mol % of xcex1-olefin units with not. more than 4 carbon atoms and from 0.01 to 1 mol % of silyl groups, and (B) an organotitanium compound having a chelating ligand, wherein the blend ratio of the component (A) to the component (B), (A)/(B) falls between 99.99/0.01 and 60/40 by weight.